There is a significant need in the art for improved secondary (rechargeable) batteries having high energy density, decreased cost, improved safety, reduced thermal management and improved stability of component supply. Batteries having such improved characteristics will be useful in a variety of applications and are of particular interest for electric utility grid storage.
Electric utilities are seeking more cost effective and efficient strategies to manage energy delivery to the grid. Peak demand is frequently met by the use of relatively expensive gas turbines, which at times of low demand remain idle. Ideally, base load electrical energy production could be operated at optimum peak efficiency, with demand variations being either absorbed or delivered using some form of energy storage. Pumped hydro (PH) technology, where water is reversibly pumped from a lower to higher elevation, has been employed for such energy storage, where round-trip efficiency is typically 68%. However, acceptable sites for implementation of PH energy storage, based upon location and environmental concerns, are now very limited. An alternatively is the use of large storage batteries, where round-trip energy conversion efficiencies can exceed that of PH, and wherein siting is not limited by geography. The market for storage batteries for this application is expected to grow, provided that battery costs are reduced and performance is increased. Major issues that are currently limiting implementation of advanced battery systems for grid storage include: overall cost for materials and associated hardware, long-term availability of materials, safety, achieving long cycle life and thermal management during operation. The present invention provides an improved battery to meet these requirements. The batteries of the invention incorporate no toxic materials, and are generally safer than comparable battery systems (e.g., sodium-sulfur systems).
Improved secondary batteries will also provide particular benefit for applications to electric vehicles and their use will translate into greater range for such vehicles.
U.S. Pat. No. 3,988,163 relates to a secondary battery having a molten sodium negative reactant, a sulfur and mixture of metal halides positive reactant melt, a carbon powder dispersed within the positive reactant melt, a solid member separating the negative reactant and the positive reactant, and a molten electrolyte on the positive reactant side of the solid member which is said to comprise a molten sodium haloaluminate. The solid member is said to be selectively-ionically conductive to sodium cations. The positive reactant is said to comprise molten sulfur and a molten mixture of metal halides. The metal halides are required to be “soluble to some extent in the sodium haloaluminate electrolyte of the battery”. Molten sodium haloaluminate is defined as “materials which include sodium halides, as for example, chlorides, bromides, fluorides, or iodides or sodium, and aluminum halides, for example, chlorides, bromides, fluorides or iodides of aluminum.” Preferred metal halides are said to be aluminum chloride and antimony chloride. The positive reactant compartment of the battery is described as containing “electrolyte-sulfur mixture of metal halides positive reactant melt” and, more specifically as “sodium chloroaluminate-sulfur, aluminum chloride and antimony chloride melt.” The battery is reported to operate at temperatures ranging from 150 to 225° C.
U.S. Pat. No. 3,877,984 relates to a secondary battery having a molten alkali metal negative reactant. a metal chloride positive reactant, a molten alkali metal chloraluminate electrolyte and a selectively-ionically-conductive separator positioned between the negative and the positive reactants. Metal chloride, sodium chloride and aluminum trichloride are combined in the positive reactant chamber and heated to form a melt. Exemplified metal chloride positive reactants included antimony chloride, ferric chloride and cupric chloride. The battery is reported to operate at temperatures ranging from 180 to 200° C.
U.S. Pat. No. 4,452,777 relates to an electrochemical cell having a sodium anode assembly, an alkali metal aluminum tetrahalide electrolyte where the cathode material is a transition metal chalcogenide or a reaction product of the chalcogenide with the electrolyte. The cathode material is described as being dispersed on a substrate which is inert under cell operating conditions. Exemplary substrates are carbon felt and nickel mesh. The preferred transition metal chalcogenide is reported to be VS2. Exemplary cells are reported to be operated at 165° C. or 170° C.
U.S. Pat. No. 5,476,733 reports a high temperature (200-400° C.) rechargeable electrochemical power storage cell where the anode compartment contains sodium active anode material, and the cathode compartment contains a sodium aluminum chloride molten salt electrolyte and a solid cathode comprising an electrolyte permeable porous matrix impregnated with the molten salt electrolyte which has solid active cathode material dispersed therein. The cell is operated at a temperature where sodium and the molten salt electrolyte are molten. The electrolyte is described as “a substantially equimolar mixture of sodium chloride and aluminium chloride in which the proportion of aluminium chloride in all states of charge is at most 50% on a molar basis.” The active cathode material is described as comprising at least one transition metal selected from the group consisting of Fe, Ni, Cr, Co, Mn, Cu and Mo having, dispersed therein, at least one additive element. In the description and the examples, the at least one additive element is said to be selected from the group consisting of As and Sb where the atomic ratio of transition metal to additive element in the active cathode material being 90:1-30:70. Only in the Abstract is the additive element said to be selected from the group consisting of As, Bi, Sb, Se and Te. The cathode is further described as “may contain, in addition, 2-12% by mass, based on the charged active cathode material, of sodium fluoride dopant and/or a sulfur-containing dopant whose sulfur forms 0.3-5% of the charged active cathode material by mass.”
U.S. Pat. No. 5,462,818 relates to an electrochemical cell where the cathode is graphite immersed in molten NaAlCl4, the anode is liquid sodium and β alumina is the sodium ion conducting solid electrolyte separating the anode and cathode compartments. The cathode is reported to contain 20 wt % graphite.
U.S. Pat. No. 8,343,661 reports a rechargeable electrochemical cell having a cathode composition comprising certain transition metals, alkali halometallate, alkali halide, a source of Zn and a source of chalcogenide. The source of Zn and that of chalcogenide is reported may be effective to improve the extractive capacity of the cell and to decrease cell resistance. Operating temperatures for the cell are reported to range from 200 to 500° C.
U.S. Pat. No. 8,445,134 relates to an electrochemical cell for a secondary battery including a positive electrode having an intercalation cathode material of bentonite. The bentonite is described as treated with acid or treated to form a polyanilie-intercalated bentonite. The cell contains an anode material containing one of magnesium and sodium and an electrolyte between the positive electrode and the negative electrode. When the anode material contains sodium, the electrolyte is a salt electrolyte, and both the anode material and the electrolyte are molten at the operating temperature of the battery.
U.S. Pat. No. 8,980,459 relates to cells and batteries employing a transition metal chalogenide positive electrode in combination with a liquid alkali metal haloaluminate electrolyte. Cells having an alkali metal negative electrode in combination with the positive electrode are reported.
Bucher et al. (2013) J. Solid State Chem. 17(7) 1923-1929 reports the use of certain sodium manganese oxides and sodium manganese cobalt oxides as cathodes for sodium ion batteries. Comprise a film containing the oxide and an organic binder on aluminum foil. The anodes employed are sodium metal and the electrolyte is a solution of NaAlCl4 (1M) in organic solvent (propylene carbonate). Caballero et al. (2002) J. Mat. Chem. 12:1142-1147 reports the use of Na0.6 MnO2 as cathodes in similar sodium ion cells.
U.S. published patent applications US2015/0093644 (published Apr. 2, 2015) and US2015/0111097 (published Apr. 23, 2015) relate to certain composite transition metal oxides which contain sodium which are reported to be useful as positive electrode material in sodium batteries. A positive electrode film formed from a mixture of the composite oxide with a conductor, a binder and a solvent is reported. Cells reported are described as having an organic electrolyte. The '644 application reports a composite oxide of formula:NaxMayMnzMbvO2+d wherein, 0.2≤x≤1, 0<y≤0.2, 0<z≤1, 0≤v<1, 0<z+v≤1, −0.3≤d<1, Ma is an electrochemically inactive metal, and Mb is different from Ma and Mn, and is at least one transition metal selected from elements in Groups 4 to 12 of the periodic table of the elements. The '097 application reports a composite oxide including sodium and a first and second transition metal having certain first and second diffraction peaks with a ratio of the first and second diffraction peaks of about 7 or greater.
U.S. published patent application US 2015/0147619 (published May 28, 2105) relates to a molten sodium battery having certain molten salt electrolytes that melt at temperatures between 100-200° C.
While electrochemical cells employing a molten sodium metal anode, a molten electrolyte and electroactive cathode materials have been reported, there remains a significant need in the art for electrochemical cells, particularly those that are rechargeable, which exhibit properties useful in a given application, such as useful levels of charge capacity and useful levels of energy density, which can be operated at practically useful temperatures, and which have enhanced safety and decreased cost. The present invention provides such electrochemical cells.